Dear All, List and IO are both monads when appropriate operations are defined.
The IO monad, which is a one-way monad, does not have a function of type IO a -> a, in general, except an unsafe function "unsafePerformIO :: IO a -> a". A two-way monad, such as List, has such a function "head :: [a] -> a". My rough question is: Is there any intersting theory on the relationship between one-way monads and two-way monads? For example, a restriction on the IO monad would offer a *safe* "unsafePerformIO", and so the IO monad would become a two-way monad. Does this question make sense at all? Thanks in advance. Kwanghoon Choi _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
